The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for a chemical mechanical polishing apparatus.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a "standard" pad or a fixed-abrasive pad. A standard pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a containment media. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad. The polishing slurry tends to be abrasive and corrosive, and can damage the mechanical parts inside the carrier head.
The substrate is typically vacuum-chucked to the underside of the carrier head at certain times during the polishing process, such as when the substrate is to be moved between polishing stations. However, the stress applied to the substrate during the vacuum-chucking procedure, particularly as the substrate is lifted off the polishing pad, may damage the substrate, e.g., the substrate may fracture. Also, it is possible for the substrate to become detached from the carrier head, e.g., when the carrier head is being moved between polishing stations, if the substrate is not properly chucked. If the substrate drops, it may be damaged when it falls.
Accordingly, it would be useful to provide a carrier head capable of reliably lifting the substrate off the polishing pad. It would also be useful if the interior of the carrier head was not exposed to contamination by slurry.